JPH11206122A - Dc-dc converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent an adverse effect on an AM radio unit mounted on a vehicle and the like, by cutting high frequency components of AC voltage output from a transformer and generating a rounded AC voltage waveform. SOLUTION: A waveform shaping circuit 6 is provided with a resistor 18 for low pass filtering with its one end connected to one end of a secondary coil 11 which constitutes a transformer 5 and the other end connected to an output terminal 17, a resistor 20 for low pass filtering with its one end connected to the other end of the secondary coil 11 and the other end connected to an output terminal 19, and a capacitor 21 for low pass filtering connected between the other ends of the resistors 18, 20. High frequency components of AC voltage outputted from the secondary coil 11 are cut and a rounded AC voltage waveform is generated and then is supplied as filament voltage Vf to a fluorescent character display tube. By this method, radiant noise can be remarkably reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC / DC converter device suitable for driving a fluorescent display tube and the like, and more particularly to a DC / DC converter for reducing radiation noise generated when driving a fluorescent display tube and the like. Related to the device.

[0002]

2. Description of the Related Art As a DC / DC converter for a fluorescent display tube, which supplies a driving voltage to a fluorescent display tube used for a light source for a meter panel of an automobile, a conventional display device shown in FIG.
Is known.

A DC / DC converter device 101 for a fluorescent display tube shown in FIG. 1 includes a transistor 102, two resistors 103 and 104, and a capacitor 105, and has a negative electrode connected to a ground line 106. Oscillation circuit 10 for generating a pulse voltage by intermitting a DC power supply voltage output from a positive electrode 107
8 is provided. The oscillation circuit 108 includes one iron core 109, one primary coil 110, one feedback coil 111, and two secondary coils 112 and 113.
The transformer 114 is provided with a voltage conversion transformer 114 that transforms the pulse voltage generated by the above to generate two AC voltages (secondary voltages) and outputs one of them as the filament voltage Vf of the fluorescent display tube. Furthermore, three diodes 115
117, and a rectifying and smoothing circuit 121 that rectifies and smoothes the other AC voltage output from the transformer 114 to generate two DC voltages Va and Vb.

[0004] The DC / DC converter device 101 for a fluorescent display tube includes a feedback coil 11 of a transformer 114.
A pulse voltage is generated by the oscillation circuit 108 based on the feedback voltage output from the power supply 1 and the DC power supply voltage output from the positive electrode of the battery 107.
14 to the primary coil 110 and the transformer 11
4 is output as a filament voltage Vf from the secondary coil 112 of the secondary coil 112 of the secondary coil 112 of the transformer 114.
3 rectifies and smoothes the other AC voltage and outputs two DC voltages Va and Vb.

[0005]

In such a conventional DC / DC converter 101 for a fluorescent display tube, a DC voltage output from a battery 107 is intermittently switched by an oscillation circuit 108 to generate a pulse voltage. Since the secondary voltage is induced in the secondary coil 112 of the transformer 114 to generate the filament voltage Vf, the filament voltage Vf becomes a square wave as shown in FIG. When supplied to a pipe, there is a problem that radiated noise is increased and adversely affects an AM radio device mounted on a car.

Accordingly, a DC / DC converter device for a fluorescent display tube which can solve such a problem has been proposed.
DC / DC converter device 12 for a fluorescent display tube shown in FIG.
Two have been proposed.

The DC / DC converter 122 for a fluorescent display tube shown in FIG. 1 is a transistor 1 of the oscillation circuit 108 which constitutes the DC / DC converter 101 shown in FIG.
02, a capacitor 123 is connected, the waveform of the pulse voltage generated by the transistor 102 is rounded, and the waveform of the secondary voltage output from the secondary coil 112 of the transformer 114 is rounded.
This prevents the filament voltage Vf output from the device from adversely affecting the AM radio device and the like.

[0008] However, the DC /
In the DC converter device 122, although the filament voltage Vf output from the secondary coil 112 can prevent the AM radio device and the like from being adversely affected, the DC voltage is provided in the oscillation circuit 108 by the charge / discharge current of the capacitor 123. Since an excessive current flows through the transistor 102, the amount of heat generated by the transistor 102 is increased, which causes a problem that reliability of the transistor 102 is reduced.

Therefore, a DC / DC converter device for a fluorescent display tube which can solve such a problem has been proposed.
DC / DC converter device 12 for a fluorescent display tube shown in FIG.
4 have been proposed.

The DC / DC converter device 124 for a fluorescent display tube shown in FIG. 1 is provided with a transformer 125 separately from the transformer 114 of the DC / DC converter device 101 shown in FIG.
An oscillation circuit 130 including one resistor 128 and one capacitor 129 is provided.
And the oscillating circuit 108 and the rectifying / smoothing circuit 121 transform the DC voltage output from the battery 107 to generate two DC voltages Va and Vb. By generating a sine wave from the DC voltage output from the battery 107 and transforming the sine wave to generate the filament voltage Vf, the filament voltage Vf output from the transformer 125 does not adversely affect the AM radio device and the like. I have to.

However, this DC / D for a fluorescent display tube is used.
In the C converter 124, one transformer 125 and one oscillation circuit 130 need to be used in addition to the DC / DC converter 101 for a fluorescent display tube shown in FIG. There is a problem that it becomes expensive.

[0012] In view of the above circumstances, the present invention can round off the filament voltage waveform and greatly reduce radiated noise without imposing a load on an oscillation circuit or the like, whereby an AM mounted on an automobile or the like can be reduced. DC / DC that can prevent adverse effects on radio equipment, etc.
It is intended to provide a converter device.

[0013]

To achieve the above object, according to the present invention, a DC voltage is converted to an AC voltage by an oscillation circuit, and the AC voltage is transformed by a transformer to convert the AC voltage. The generating DC / DC converter device is characterized in that it has a waveform shaping circuit that cuts a high-frequency component of the AC voltage output from the transformer and generates an AC voltage waveform with rounded corners.

[0014] According to a second aspect of the present invention, the D
In the C / DC converter device, the waveform shaping circuit includes a low-pass filter including at least one resistor and one capacitor, and cuts a high-frequency component in an AC voltage output from the transformer by the low-pass filter. Features.

According to the first aspect of the present invention, a high-frequency component of the AC voltage output from the transformer is cut by the waveform shaping circuit to generate an AC voltage waveform with rounded corners, thereby providing an oscillation circuit or the like. Without burdening the system, the filament voltage Vf is rounded to significantly reduce radiated noise, thereby preventing an AM radio device mounted on an automobile or the like from being adversely affected.

Further, the waveform shaping circuit has at least one
By forming a low-pass filter from one resistor and one capacitor to cut high-frequency components in the AC voltage output from the transformer, radiation noise can be reduced while keeping the cost of the device itself low. Become.

[0017]

FIG. 1 shows a DC / DC converter device for a fluorescent display according to an embodiment of the present invention.
It is a circuit diagram of a C converter device.

The DC / DC converter device 1 for a fluorescent display tube shown in FIG. 1 generates a pulse voltage by interrupting a DC power supply voltage output from a positive electrode of a battery 3 having a negative electrode connected to a ground line 2. Oscillating circuit 4, a transformer 5 for converting a pulse voltage generated by the oscillating circuit 4 to generate two AC voltages (secondary voltages), and one AC output from the transformer 5 A waveform shaping circuit 6 for generating a filament voltage Vf of the fluorescent display tube by rounding the voltage waveform, and a rectifying and smoothing circuit 7 for rectifying and smoothing the other AC voltage output from the transformer 5 to generate two DC voltages. Have. Then, based on the feedback voltage output from the feedback coil 10 of the transformer 5 and the DC power supply voltage output from the positive electrode of the battery 3,
A pulse voltage is generated by the oscillating circuit 4 and supplied to the primary coil 9 of the transformer 5 to output an AC voltage from each of the secondary coils 11 and 12 of the transformer 5. Is rounded to generate the filament voltage Vf of the fluorescent display tube, and the other of the AC voltages is rectified and smoothed by the
And two DC voltages Va and Vb.

The transformer 5 takes in an iron core 8 composed of a magnetic member having a predetermined shape and a pulse voltage wound around the iron core 8 and output from the oscillation circuit 4. And a feedback coil 10 wound around the iron core 8 and generating a feedback voltage (secondary voltage) based on the AC magnetic flux generated in the iron core 8. The secondary coil 11 is wound around the iron core 8 to generate an AC voltage (secondary voltage) based on the AC magnetic flux generated in the iron core 8 and supply the AC voltage (secondary voltage) to the waveform shaping circuit 6. A secondary coil 12 is provided which generates an AC voltage (secondary voltage) based on the AC magnetic flux generated in the iron core 8 and supplies the AC voltage (secondary voltage) to the rectifying / smoothing circuit 7. Then, an AC magnetic flux is generated in the iron core 8 by the primary coil 9 based on the pulse voltage supplied from the oscillation circuit 4, and the feedback coil 1
0, while generating a secondary voltage in each of the secondary coils 11 and 12, the secondary voltage generated in the feedback coil 10 is used as a feedback voltage and fed back to the oscillation circuit 4, and each secondary coil 1
The respective secondary voltages generated at 1 and 12 are supplied to the waveform shaping circuit 6 and the rectifying / smoothing circuit 7, respectively.

The oscillating circuit 4 includes a transistor 13 for interrupting the DC voltage output from the battery 3 to supply a pulse voltage to the primary coil 9 of the transformer 5 and a transistor 13 for converting the DC voltage output from the battery 3 to a transistor. 13, a bias resistor 14 for biasing the transistor 13 and a feedback coil 1 of the transformer 5.
Oscillator capacitor 15 charged by the feedback voltage output from 0, and oscillating resistor 16 that supplies the voltage charged in capacitor 15 and the feedback voltage output from feedback coil 10 to the base of transistor 13.
And Then, the DC voltage output from the battery 3 is guided to the base of the transistor 13 by the resistor 14, and while biasing the transistor 13,
The feedback voltage output from the feedback coil 10 of the transformer 5 by the capacitor 15 and the resistor 16 is
And oscillates it, and supplies the pulse voltage obtained by this to the primary coil 9 of the transformer 5.

The waveform shaping circuit 6 has one end connected to one end of the secondary coil 11 constituting the transformer 5, the other end connected to an output terminal 17, a low-pass filtering resistor 18, and one end connected to the secondary coil 11. Connected to the other end of the coil 11,
The other end includes a low-pass filtering resistor 20 connected to the output terminal 19, and a low-pass filtering capacitor 21 connected to the other end of each of the resistors 18 and 20. The waveform shaping circuit 6 cuts the high frequency component of the AC voltage output from the secondary coil 11 as shown in FIG. 2A, and rounds the corner as shown in FIG. The generated AC voltage waveform is supplied to the fluorescent display tube as the filament voltage Vf of the fluorescent display tube.

The rectifying / smoothing circuit 7 is connected to the transformer 5
Three diodes 22 to 24 for rectifying the secondary voltage obtained by the secondary coil 12 to generate a DC voltage, and smoothing the DC voltage obtained by each of the diodes 22 to 24 to obtain two DC voltages Va and Vb. Are generated. The rectifying / smoothing circuit 7 includes diodes 22 to 24 and capacitors 25
27 rectify and smooth the secondary voltage output from the secondary coil 12 of the transformer 5 to obtain two DC voltages Va,
Vb is generated and supplied to a fluorescent display tube driving circuit and the like.
By biasing the next coil 11, the filament voltage Vf output from the waveform shaping circuit 6 is shifted to the positive potential side.

As described above, in this embodiment, 2
The waveform of the rectangular AC voltage output from the secondary coil 11 of the transformer 5 is shaped by an extremely inexpensive waveform shaping circuit 6 composed of two resistors 18 and 20 and one capacitor 21 to round the corners. Since the filament voltage Vf of the fluorescent display tube is generated, the corners of the filament voltage Vf can be rounded without increasing the cost of the device itself, without burdening the oscillation circuit 4 and the like, and radiation noise can be greatly reduced. Therefore, it is possible to prevent an adverse effect on an AM radio device mounted on an automobile or the like.

[0024]

As described above, according to the present invention, D
In the C / DC converter device, it is possible to reduce the radiation noise greatly by rounding the filament voltage Vf without putting a burden on the oscillation circuit while keeping the cost of the device itself low. It does not adversely affect the AM radio device or the like that is used.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a DC / DC converter device for a fluorescent display tube showing an embodiment of a DC / DC converter device according to the present invention.

FIG. 2 is a waveform chart for explaining a waveform shaping operation of the waveform shaping circuit shown in FIG. 1;

FIG. 3 shows a conventionally known DC / DC for a fluorescent display tube.
It is a circuit diagram showing an example of a converter device.

4 is a waveform diagram illustrating an example of a filament voltage output from the DC / DC converter device for a fluorescent display tube illustrated in FIG.

FIG. 5 shows another conventional DC / DC for a fluorescent display tube.
It is a circuit diagram showing an example of a DC converter device.

FIG. 6 shows another conventional DC / DC for a fluorescent display tube.
It is a circuit diagram showing an example of a DC converter device.

[Explanation of symbols]

 1: DC / DC converter device for fluorescent display tube 2: ground line 3: battery 4: oscillation circuit 5: transformer 6: waveform shaping circuit 7: rectifying and smoothing circuit 8: iron core 9: primary coil 10: feedback coil 11, 12 : Secondary coil 13: Transistor 14, 16, 18, 20: Resistance 15, 21, 25-27: Capacitor 17, 19: Output terminal 22-24: Diode

Claims (2)

[Claims] 1. A DC / DC converter device for converting a DC voltage into an AC voltage by an oscillation circuit and transforming the AC voltage by a transformer to generate an AC voltage, wherein a high-frequency component of the AC voltage output from the transformer is A DC / DC converter device comprising a waveform shaping circuit that generates an AC voltage waveform that is cut and rounded. 2. The DC / DC converter device according to claim 1, wherein the waveform shaping circuit is configured by a low-pass filter including at least one resistor and one capacitor, and is output from the transformer by the low-pass filter. DC characterized by cutting high frequency components in AC voltage
/ DC converter device.